Make a read splice from a DAX file go directly to copy_splice_read() to do
the reading as filemap_splice_read() is unlikely to find any pagecache to
splice.
I think this affects only erofs, Ext2, Ext4, fuse and XFS.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Christoph Hellwig <hch@xxxxxx>
cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
cc: Jens Axboe <axboe@xxxxxxxxx>
cc: linux-erofs@xxxxxxxxxxxxxxxx
cc: linux-ext4@xxxxxxxxxxxxxxx
cc: linux-xfs@xxxxxxxxxxxxxxx
cc: linux-fsdevel@xxxxxxxxxxxxxxx
cc: linux-block@xxxxxxxxxxxxxxx
cc: linux-mm@xxxxxxxxx